1. Field of the Invention
The present invention relates to a process for the synthesis of [beta]-cyanoketones, in particular 3-cyano-3,5,5'-trimethyl-1-cyclohexanone, starting from isophorone and alkaline cyanides or solutions thereof.
3-cyano-3,5,5'-trimethyl-1-cyclohexanone is the chemical precursor of an important substance, isophorondiamine, which is notoriously used as hardener for epoxy resins and as monomer in the synthesis of polyurethane and polyamide resins.
2. Prior Art
General methods for preparing cyanoketones which provide the 1:4 addition of hydrocyanic acid to the [alpha][beta]-unsaturated ketone are known. The reaction is usually performed in the presence of catalytic amounts of alkaline substances capable of forming cyanide ions. The use of hydrocyanic acid, which is not always easily available, entails problems in handling due to its highly toxic nature.
Therefore, despite the good results which can be achieved with hydrocyanic acid, attempts have nonetheless been made to use directly the more manageable cyanide solutions which however penalize reaction times and yields.
In the European patent application EP 0028179, an attempt has been made to improve the yields of the synthesis by means of a two-phase system. This patent application provides a process in which the organic isophorone solution is placed in contact with the aqueous cyanide solution in the presence of catalytic amounts of a phase transfer agent such as for example quaternary ammonium or phosphonium salts. Yields and reaction times are acceptable, but the amounts of cyanide necessarily used in great excess with respect to the stoichiometric requirement make the process difficult to apply on an industrial scale. This synthesis system, besides being economically negative, in fact creates considerable problems in inertizing the effluents.
It has been so far possible to synthesize 3-cyano-3,5,5'-trimethyl-1-cyclohexanone from isophorone and cyanide in a convenient manner only by resorting to great cyanide excesses.